Disorders of Water and Salt Metabolism Endocrinol Metab Clin N AmAssociated

Disorders of water and sodium homeostasis are very common problems en-countered in clinical medicine. Disorders of water metabolism are divided into hyperosmolar and hypoosmolar states, with hyperosmolar disorders charac-terized by a deficit of body water in relation to body solute, and hypoosmolar disorders characterized by an excess of body water in relation to total body solute. Because sodium is the main constituent of plasma osmolality, these disorders are typically characterized by hypernatremia and hyponatremia, respectively. Hyponatremia is far more common, occurring at prevalences as high as 6 % to 22 % of hospitalized patients [1], and has been associated withmortality rates from 0 % to 50%, depending on the acuteness and severity of the hyponatremia. Hypernatremia has a prevalence of only 1 % of hospital-ized patients, but is associated with highmortality rates, from 42 % to 60 % [2]. In the setting of intrasellar and suprasellar lesions, excessive water loss from diabetes insipidus is more likely than inappropriate water retention from the syndrome of inappropriate antidiuretic hormone secretion (SIADH), although both can occur following surgical resection of these lesions. This article briefly reviews the physiology of hyperosmolar and hy-poosmolar syndromes, then focuses on a discussion of the pathophysiology, evaluation, and treatment of specific pre- and postoperative disorders of water metabolism in patients with pituitary lesions. Overview of normal water metabolism Water metabolism is controlled primarily by arginine vasopressin (AVP),37 (2008) 213–234a nonapeptide that is synthesized in the neurohypophyseal magnocellular * Corresponding author